FortiOS 6 – Data leak prevention

Data leak prevention

The FortiGate data leak prevention (DLP) system allows you to prevent sensitive data from leaving your network. When you define sensitive data patterns, data matching these patterns will be blocked, or logged and allowed, when passing through the FortiGate unit. You configure the DLP system by creating individual filters based on file type, file size, a regular expression, an advanced rule, or a compound rule, in a DLP sensor and assign the sensor to a security policy.

Although the primary use of the DLP feature is to stop sensitive data from leaving your network, it can also be used to prevent unwanted data from entering your network and to archive some or all of the content passing through the FortiGate unit.

This section describes how to configure the DLP settings. DLP can only be configured for FortiGate units in proxybased inspection.

Data leak prevention concepts

Data leak prevention examines network traffic for data patterns you define through the use of the GUI and CLI commands. The DLP feature is broken down into a number of parts. Note, DLP is not available in flow-based inspection.

DLP sensor

A DLP sensor is a package of filters. To use DLP, you must enable it in a security policy and select the DLP sensor to use. The traffic controlled by the security policy will be searched for the patterns defined in the filters contained in the DLP sensor. Matching traffic will be passed or blocked according to how you configured the filters.

DLP filter

Each DLP sensor has one or more filters configured within it. Filters can examine traffic for known files using DLP fingerprints, for files of a particular type or name, for files larger than a specified size, for data matching a specified regular expression, or for traffic matching an advanced rule or compound rule.

DLP filter actions

You can configure the action taken when a match is detected. The actions include:

l Allow l Log Only l Block l Quarantine IP address

Log Only is enabled by default.

Allow

No action is taken even if the patterns specified in the filter are matched.

Log Only

The FortiGate unit will take no action on network traffic matching a rule with this action. The filter match is logged, however. Other matching filters in the same sensor may still operate on matching traffic.

Block

Traffic matching a filter with the block action will not be delivered. The matching message or download is replaced with the data leak prevention replacement message.

Quarantine IP Address/ Source IP ban

Starting in FortiOS 5.2, the quarantine, as a place where traffic content was held in storage so it couldn’t interact with the network or system, was removed. The term quarantine was kept to describe preventing selected source IPs from interacting with the network and protected systems. This source IP ban is kept in the kernel rather than in any specific application engine and can be queried by APIs. The features that can use the APIs to access and use the banned source IP addresses are antivirus, DLP, DoS and IPS. Both IPv4 and IPv6 version are included in this feature.

If the quarantine-ip action is used, the additional variable of expiry time will become available. This variable determines for how long the source IP address will be blocked. In the GUI it is shown as a field before minutes. In the CLI the option is called expiry and the duration is in the format <###d##h##m>. The maximum days value is 364. The maximum hour value is 23 and the maximum minute value is 59. The default is 5 minutes.

If a DLP sensor has contains a DLP filter with action set to Allow certain files and another DLP filter with action set to Block those same files, then the order of the filters within that sensor will determine which action is taken first.

Configuring using the CLI

To configure the DLP sensor to add the source IP address of the sender of a protected file to the quarantine or list of banned source IP addresses edit the DLP Filter, use these CLI commands:

Preconfigured sensors

A number of preconfigured sensors are provided with your FortiGate unit. These can be edited to more closely match your needs.

Two of the preconfigured sensors with filters ready for you to enable are:

Credit-Card – This sensor logs the traffic, both files and messages, that contain credit card numbers in the formats used by American Express, MasterCard and Visa.

SSN-Sensor – This sensor logs the traffic, both files and messages, that contain Social Security Numbers with the exception of those that are WebEx invitation emails.

DLP document fingerprinting

One of the DLP techniques to detect sensitive data is fingerprinting (also called document fingerprinting). Most DLP techniques rely on you providing a characteristic of the file you want to detect, whether it’s the file type, the file name, or part of the file contents. Fingerprinting is different in that you provide the file itself. The FortiGate unit then generates a checksum fingerprint and stores it. The FortiGate unit generates a fingerprint for all files detected in network traffic, and it is compared to all of the fingerprints stored in its fingerprint database. If a match is found, the configured action is taken.

Any type of file can be detected by DLP fingerprinting and fingerprints can be saved for each revision of your files as they are updated. To use fingerprinting you:

l select the documents to be fingerprinted l add fingerprinting filters to DLP sensors l add the sensors to firewall policies that accept the traffic to which to apply fingerprinting.

Fingerprinting

Fingerprint scanning allows you to create a library of files for the FortiGate unit to examine. It will create checksum fingerprints so each file can be easily identified. Then, when files appear in network traffic, the FortiGate will generate a checksum fingerprint and compare it to those in the fingerprint database. A match triggers the configured action.

You must configure a document source or uploaded documents to the FortiGate unit for fingerprint scanning to work.

Fingerprinted documents

The FortiGate unit must have access to the documents for which it generates fingerprints.

Configuring the document source

To configure a DLP fingerprint document source in FortiOS 5.6.0, you must use CLI commands.

Once you have set the document source and configured the DLP sensor for fingerprinting, add the DLP sensor to the applicable firewall policy. This can be done through the GUI.

File size

This filter-type checks for files exceeding a configured size. All files larger than the specified size are subject to the configured action. The value of the field is measured in kilobytes (KB).

Data leak prevention concepts

DLP filtering by specific file types

File filters use file filter lists to examine network traffic for files that match either file names or file types. For example, you can create a file filter list that will find files called secret.* and also all JPEG graphic files. You can create multiple file filter lists and use them in filters in multiple DLP sensors as required.

Specify File Types is a DLP option that allows you to block files based on their file name or their type.

File types are a means of filtering based on examination of the file contents, regardless of the file name. If you block the file type Archive (zip), all zip archives are blocked even if they are renamed with a different file extension. The FortiGate examines the file contents to determine what type of file it is and then acts accordingly.

File Name patterns are a means of filtering based purely on the names of files. They may include wildcards (*). For example, blocking *.scr will stop all files with an .scr file extension, which is commonly used for Windows screen saver files. Files trying to pass themselves off as Windows screen saver files by adopting the file-naming convention will also be stopped.

Files can specify the full or partial file name, the full or partial file extension, or any combination. File pattern entries are not case sensitive. For example, adding *.exe to the file pattern list also blocks any files ending with .exe. l Files are compared to the enabled file patterns from top to bottom, in list order.

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